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Night Vision

26 October 2006

A point was made in class yesterday that cameras (unlike active sensors such as sonar) are poor in low-light conditions. The amateur astronomer in me took exception to this; anyone who has seen the Hubble Deep Field knows what I mean.

So I ran my own 'deep field' experiment:

	Here's a pumpkin photographed with the overhead light switched on. Looks ok.
	Here's the same pumpkin photographed with the overhead light switched off. To the human eye, it's pitch black. But it's not...
	The above dark photograph can be artificially brightened and contrast stretched (using the Gimp). This reveals the subject matter, but it contains a huge amount of noise. View the full image for a better look.
	A better way to enhance the image is to take 75 separate dark photographs, then stack them on top of each other. This is equivalent to taking one image with a 75x exposure time. Noise is no longer a problem since it averages out. The only issue is that my camera's bad pixels become blatantly obvious. Actually, those bad pixels were just as bright in the previous image, but they weren't noticable due to all the noise. View the full image for a better look.

Long exposures (or image stacking) can turn night into day. Unless one is in a hurry, cameras are quite effective regardless of the light levels.

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